Filter calibration and applications thereof

ABSTRACT

A method for calibrating a filter begins with the filter filtering a first signal having a first frequency to produce a first filtered signal, wherein the first frequency is in a known pass region of the filter. The processing continues by measuring signal strength of the first filtered signal to produce a first measured signal strength. The processing continues with the filter filtering a second signal having a second frequency to produce a second filtered signal, wherein the second frequency is at a desired corner frequency of the filter. The processing continues by measuring signal strength of the second filtered signal to produce a second measured signal strength. The processing continues by comparing the first measured signal strength with the second measured signal strength to determine whether the filter has attenuated the second signal by a desired attenuation value with respect to the first signal. The processing continues by adjusting filter response of the filter to produce an adjusted filter response when the filter has not attenuated the second signal by the desired attenuation value with respect to the first signal.

BACKGROUND OF THE INVENTION

1. Technical Field

This invention relates generally to integrated circuits and moreparticularly to calibration of circuits of the integrated circuit.

2. Description of Related Art

Integrated circuits are known to be used in a wide variety of electronicequipment including radios, cellular telephones, wireless modems, homeappliances, etc. One common technology for producing integrated circuitsis Complimentary Metal Oxide Semiconductor, which is more commonly knownas CMOS. CMOS technology has become the fabrication technology of choicefor a majority of commercial grade integrated circuits due to itsflexibility of design, level of integration, and cost.

While CMOS technology offers many advantages, there are somelimitations. For instance, component tolerances of on-chip resistors,capacitors, and/or transistors are at best +/−5%, but more typically+/−20%. For many circuits, the component tolerance is not a criticalissue, however, for precision circuit the component tolerance is acritical issue. For example, a resistor-capacitor (e.g., RC) low passfilter passes signals having frequencies below a corner frequency of thelow pass filter and attenuates signals having frequencies above thecorner frequency. As is known, the corner frequency is established basedon the resistance value and capacitance value. With component tolerancesof +/−20%, the corner frequency of a single pole RC low pass filter(i.e., a low pass filter that includes a single resistor and a singlecapacitor) may vary from 0.64 of the desired corner frequency when the Rand C are each at the minimum component value to 1.44 of the desiredcorner frequency when the R and C are each at the maximum componentvalue. This wide variation is unacceptable.

To reduce the adverse affects of the component tolerance variation, manyCMOS integrated circuit (IC) designs include an RC calibration circuitand selectable resistor circuits and capacitor circuits for use inprecision circuits. In general, the RC calibration circuit includes atest resistor and a test capacitor. The test resistor and test capacitorare tested, typically by applying a voltage, a pulse, and/or a ramp, todetermine their actual values. The actual values are compared to thedesigned values to determine a difference. The difference is used totune the selectable resistor circuits and capacitor circuits. Forexample, if the test resistor was designed to be a 1 Kilo-Ohm resistorand it is measured to be 900 Ohms, the actual value is 90% of thedesired value. To achieve the desired value, the actual value must beincreased by 1.11 (e.g., 1/0.9). Thus, the selectable resistor andcapacitor circuits are adjusted by a value of 1.11.

While the RC calibration circuits allow for precision circuits to beimplemented on ICs using CMOS technology, they are based on theassumption that the components of the IC have the same component offsetas the test components. In many applications, this assumption is of noconsequence. For highly precise circuits, such as low pass filters usedin radio receivers to block local oscillation leakage, the RCcalibration circuit are not sufficiently accurate.

Therefore, a need exists for a method and apparatus to calibrate highlyprecise IC circuits including filters.

BRIEF SUMMARY OF THE INVENTION

The filter calibration techniques of the present invention substantiallymeet these needs and others. In one embodiment, a method for calibratinga filter begins with the filter filtering a first signal having a firstfrequency to produce a first filtered signal, wherein the firstfrequency is in a known pass region of the filter. The processingcontinues by measuring signal strength of the first filtered signal toproduce a first measured signal strength. The processing continues withthe filter filtering a second signal having a second frequency toproduce a second filtered signal, wherein the second frequency is at adesired corner frequency of the filter. The processing continues bymeasuring signal strength of the second filtered signal to produce asecond measured signal strength. The processing continues by comparingthe first measured signal strength with the second measured signalstrength to determine whether the filter has attenuated the secondsignal by a desired attenuation value with respect to the first signal.The processing continues by adjusting filter response of the filter toproduce an adjusted filter response when the filter has not attenuatedthe second signal by the desired attenuation value with respect to thefirst signal. With such a method and apparatus implementing such amethod, components of a highly precise circuit on an integrated circuitmay be accurately tuned to provide the desired circuit performance.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a schematic block diagram of a wireless communication systemin accordance with the present invention;

FIG. 2 is a schematic block diagram of a wireless communication devicein accordance with the present invention;

FIG. 3 is a schematic block diagram of a filtering module withcalibration in accordance with the present invention;

FIG. 4A is a graph of a filter response of a low pass filter;

FIG. 4B is a graph of testing a low pass filter in accordance with thepresent invention;

FIG. 5A is a graph of a filter response of a high pass filter;

FIG. 5B is a graph of testing a high pass filter in accordance with thepresent invention;

FIG. 6A is a graph of a filter response of a bandpass filter;

FIG. 6B is a graph of testing a bandpass filter in accordance with thepresent invention;

FIG. 7A is a graph of a filter response of a stop band pass filter:

FIG. 7B is a graph of testing a stop band pass filter in accordance withthe present invention;

FIG. 8 is a schematic block diagram of a calibration configuration for areceiver section of a radio in accordance with the present invention;

FIG. 9 is a logic diagram of a method for calibrating a filter inaccordance with the present invention; and

FIG. 10 is a logic diagram of a method for calibrating a low pass filterin accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a schematic block diagram illustrating a communication system10 that includes a plurality of base stations and/or access points12-16, a plurality of wireless communication devices 18-32 and a networkhardware component 34. The wireless communication devices 18-32 may belaptop host computers 18 and 26, personal digital assistant hosts 20 and30, personal computer hosts 24 and 32 and/or cellular telephone hosts 22and 28. The details of the wireless communication devices will bedescribed in greater detail with reference to FIG. 2.

The base stations or access points 12-16 are operably coupled to thenetwork hardware 34 via local area network connections 36, 38 and 40.The network hardware 34, which may be a router, switch, bridge, modem,system controller, et cetera provides a wide area network connection 42for the communication system 10. Each of the base stations or accesspoints 12-16 has an associated antenna or antenna array to communicatewith the wireless communication devices in its area. Typically, thewireless communication devices register with a particular base stationor access point 12-14 to receive services from the communication system10. For direct connections (i.e. point-to-point communications),wireless communication devices communicate directly via an allocatedchannel.

Typically, base stations are used for cellular telephone systems andlike-type systems, while access points are used for in-home orin-building, wireless networks. Regardless of the particular type ofcommunication system, each wireless communication device includes abuilt-in radio and/or is coupled to a radio. The radio includes a highlylinear amplifier and/or programmable multi-stage amplifier as disclosedherein to enhance performance, reduce costs, reduce size, and/or enhancebroadband applications.

FIG. 2 is a schematic block diagram illustrating a wirelesscommunication device that includes the host device 18-32 and anassociated radio 60. For cellular telephone hosts, the radio 60 is abuilt-in component. For personal digital assistants hosts, laptop hosts,and/or personal computer hosts, the radio 60 may be built-in or anexternally coupled component.

As illustrated, the host device 18-32 includes a processing module 50,memory 52, radio interface 54, input interface 58 and output interface56. The processing module 50 and memory 52 execute the correspondinginstructions that are typically done by the host device. For example,for a cellular telephone host device, the processing module 50 performsthe corresponding communication functions in accordance with aparticular cellular telephone standard.

The radio interface 54 allows data to be received from and sent to theradio 60. For data received from the radio 60 (e.g., inbound data), theradio interface 54 provides the data to the processing module 50 forfurther processing and/or routing to the output interface 56. The outputinterface 56 provides connectivity to an output display device such as adisplay, monitor, speakers, et cetera such that the received data may bedisplayed. The radio interface 54 also provides data from the processingmodule 50 to the radio 60. The processing module 50 may receive theoutbound data from an input device such as a keyboard, keypad,microphone, et cetera via the input interface 58 or generate the dataitself. For data received via the input interface 58, the processingmodule 50 may perform a corresponding host function on the data and/orroute it to the radio 60 via the radio interface 54.

Radio 60 includes a host interface 62, digital receiver processingmodule 64, an analog-to-digital converter 66, a filtering/gain module68, an IF mixing down conversion stage 70, a receiver filter 71, a lownoise amplifier 72, a transmitter/receiver switch 73, a localoscillation module 74, memory 75, a digital transmitter processingmodule 76, a digital-to-analog converter 78, a filtering/gain module 80,an IF mixing up conversion stage 82, a power amplifier 84, a transmitterfilter module 85, and an antenna 86. The antenna 86 may be a singleantenna that is shared by the transmit and receive paths as regulated bythe Tx/Rx switch 73, or may include separate antennas for the transmitpath and receive path. The antenna implementation will depend on theparticular standard to which the wireless communication device iscompliant. The filtering/gain modules 68 and/or 80 may includecalibration circuitry as will be described with reference to FIGS. 3-10.

The digital receiver processing module 64 and the digital transmitterprocessing module 76, in combination with operational instructionsstored in memory 75, execute digital receiver functions and digitaltransmitter functions, respectively. The digital receiver functionsinclude, but are not limited to, digital intermediate frequency tobaseband conversion, demodulation, constellation demapping, decoding,and/or descrambling. The digital transmitter functions include, but arenot limited to, scrambling, encoding, constellation mapping, modulationand/or digital baseband to IF conversion. The digital receiver andtransmitter processing modules 64 and 76 may be implemented using ashared processing device, individual processing devices, or a pluralityof processing devices. Such a processing device may be a microprocessor,micro-controller, digital signal processor, microcomputer, centralprocessing unit, field programmable gate array, programmable logicdevice, state machine, logic circuitry, analog circuitry, digitalcircuitry, and/or any device that manipulates signals (analog and/ordigital) based on operational instructions. The memory 75 may be asingle memory device or a plurality of memory devices. Such a memorydevice may be a read-only memory, random access memory, volatile memory,non-volatile memory, static memory, dynamic memory, flash memory, and/orany device that stores digital information. Note that when theprocessing module 64 and/or 76 implements one or more of its functionsvia a state machine, analog circuitry, digital circuitry, and/or logiccircuitry, the memory storing the corresponding operational instructionsis embedded with the circuitry comprising the state machine, analogcircuitry, digital circuitry, and/or logic circuitry.

In operation, the radio 60 receives outbound data 94 from the hostdevice via the host interface 62. The host interface 62 routes theoutbound data 94 to the digital transmitter processing module 76, whichprocesses the outbound data 94 in accordance with a particular wirelesscommunication standard (e.g., IEEE 802.11 Bluetooth, et cetera) toproduce digital transmission formatted data 96. The digital transmissionformatted data 96 will be a digital base-band signal or a digital low IFsignal, where the low IF typically will be in the frequency range of onehundred kilohertz to a few megahertz.

The digital-to-analog converter 78 converts the digital transmissionformatted data 96 from the digital domain to the analog domain. Thefiltering/gain module 80 filters and/or adjusts the gain of the analogssignal prior to providing it to the IF mixing stage 82. The IF mixingstage 82 converts the analog baseband or low IF signal into an RF signalbased on a transmitter local oscillation 83 provided by localoscillation module 74. The power amplifier 84 amplifies the RF signal toproduce outbound RF signal 98, which is filtered by the transmitterfilter module 85. The antenna 86 transmits the outbound RF signal 98 toa targeted device such as a base station, an access point and/or anotherwireless communication device.

The radio 60 also receives an inbound RF signal 88 via the antenna 86,which was transmitted by a base station, an access point, or anotherwireless communication device. The antenna 86 provides the inbound RFsignal 88 to the receiver filter module 71 via the Tx/Rx switch 73,where the Rx filter 71 bandpass filters the inbound RF signal 88. The Rxfilter 71 provides the filtered RF signal to low noise amplifier 72,which amplifies the signal 88 to produce an amplified inbound RF signal.The low noise amplifier 72 provides the amplified inbound RF signal tothe IF mixing module 70, which directly converts the amplified inboundRF signal into an inbound low IF signal or baseband signal based on areceiver local oscillation 81 provided by local oscillation module 74.The down conversion module 70 provides the inbound low IF signal orbaseband signal to the filtering/gain module 68. The filtering/gainmodule 68 filters and/or gains the inbound low IF signal or the inboundbaseband signal to produce a filtered inbound signal.

The analog-to-digital converter 66 converts the filtered inbound signalfrom the analog domain to the digital domain to produce digitalreception formatted data 90. The digital receiver processing module 64decodes, descrambles, demaps, and/or demodulates the digital receptionformatted data 90 to recapture inbound data 92 in accordance with theparticular wireless communication standard being implemented by radio60. The host interface 62 provides the recaptured inbound data 92 to thehost device 18-32 via the radio interface 54.

As one of average skill in the art will appreciate, the wirelesscommunication device of FIG. 2 may be implemented using one or moreintegrated circuits. For example, the host device may be implemented onone integrated circuit, the digital receiver processing module 64, thedigital transmitter processing module 76 and memory 75 may beimplemented on a second integrated circuit, and the remaining componentsof the radio 60, less the antenna 86, may be implemented on a thirdintegrated circuit. As an alternate example, the radio 60 may beimplemented on a single integrated circuit. As yet another example, theprocessing module 50 of the host device and the digital receiver andtransmitter processing modules 64 and 76 may be a common processingdevice implemented on a single integrated circuit. Further, the memory52 and memory 75 may be implemented on a single integrated circuitand/or on the same integrated circuit as the common processing modulesof processing module 50 and the digital receiver and transmitterprocessing module 64 and 76.

FIG. 3 is a schematic block diagram of a filtering module 68 and/or 80that includes a filtering circuit 100 and a calibration module 102. Thefiltering circuit 100, which may be a low pass filter, a bandpassfilter, a stop band filter, or a high pass filter, includes a firstadjustable filter element 108 and a second adjustable filter element110. The particular types of components of the first and secondadjustable filter elements 108 and 110 depend on the type of filteringdesired. For example, for a low pass filter, the first adjustable filterelement 108 may be an adjustable resistor and the second adjustablefilter element 110 may be an adjustable capacitor.

The calibration module 102 includes a signal strength module 112, acomparator 114, and a response adjust module 116. In operation, a tonesignal (i.e. a signal having a single frequency component) having afrequency well within the pass region of the filtering circuit 100 isprovided to the input of the filtering circuit 100 as a received signal104. Since this tone signal is well within the pass region of thefilter, the filtered output signal 106 should substantially match theinputted tone signal. The signal strength module 112, which may be areceived signal strength indicator, measures the signal strength of thefiltered signal 106 of the first tone signal. This signal strength valueis stored within the signal strength module 112. Next, a second tonesignal is inputted to the filtering circuit 100, where second tonesignal has a frequency at a corner frequency of the filtering circuit100.

For example, if the filtering circuit 100 implements a single pole lowpass filter, the corner frequency corresponds to the −3 dB point (i.e.,the frequency at which a signal is attenuated by approximately ⅓^(rd) bythe filter with respect to an unattenuated signal) as shown in FIG. 4.While the desired corner frequency establishes the pass region (i.e.,signals having frequencies in this region are passed substantiallyunattenuated) and the attenuation region (i.e., signals havingfrequencies in this region are attenuated based on the response of thefilter). Due to limitations of the CMOS technology, a low pass filterwill most likely not have the desired corner frequency, but one that isup to forty percent from the desired corner frequency, as illustrated bythe shaded area.

Continuing with the low pass filter example, and with reference to FIG.5, the first filtered tone signal 124 has a frequency well within thepass region, thus its amplitude substantially matches the amplitude ofthe inputted tone signal. In one embodiment, to ensure that the firstfiltered tone signal 124 is within the pass region, the components ofthe filter are set to provide a maximum pass band. The second filteredtone signal 126 has a frequency at the desired corner frequency. Thesignal strength module 112 stores both signal strengths and comparesthem to establish an actual attenuation 118.

Returning to the discussion of FIG. 3, the comparator compares theactual attenuation 118 is compared with the desired attenuation 120,which for a low pass filter is −3 dB (i.e., the magnitude of the secondfiltered tone signal 126 should be approximately ⅔rds of the magnitudeof the first filtered tone signal 124). If the actual attenuation 118substantially matches the desired attenuation 120, the corner frequencyof the low pass filter is at the desired frequency. If, however, theactual attenuation 118 is greater than the desired attenuation (i.e.,the magnitude of the second filtered tone signal 126 is less than thedesired ⅔rds the amplitude of the first filtered tone signal 124), thecorner frequency is too low. In this instance, the response adjustmodule 116 generates an adjust filter response 122 that increases thevalue of the first and/or second adjustable filter element 108 and 110.Once the adjustment is made, the process is repeated until the actualattenuation 118 substantially matches the desired attenuation 120.

If the actual attenuation 118 is less than the desired attenuation 120(i.e. the magnitude of the second filtered tone signal 126 is greaterthan the desired ⅔rds the amplitude of the first filtered tone signal124), the corner frequency is too high. In this instance, the responseadjust module 116 generates an adjust filter response 122 that decreasesthe value of the first and/or second adjustable filter element 108 and110. Once the adjustment is made, the process is repeated until theactual attenuation 118 substantially matches the desired attenuation120. As such, the value of one or both of the adjustable filter elements108 and 110 may be incrementally adjusted to achieve the desiredattenuation, i.e., the desired corner frequency. Alternatively, theresponse adjust module 116 may determine the amount of differencebetween the actual attenuation 118 and the desired attenuation 120.Based on the difference, the response adjust module 116 determines theadjust filter response 122.

The calibration filter of FIG. 3 may be a low pass filter, as describedwith reference to FIG. 4, a high pass filter, a bandpass filter, or astop band filter. FIGS. 5A and 5B illustrate the calibration of a highpass filter. FIG. 5A illustrates the frequency response of a singlepole, or first order, high pass filter that includes an attenuationregion and a pass region. The desired corner frequency delineates thesetwo regions. The calibration of the high pass filter is shown in FIG.5B. The calibration begins by providing a first tone signal that has afrequency well within the pass region. The filtered first tone signal124 is shown to have a first magnitude, or signal strength. Thecalibration continues by providing a second tone signal that has afrequency at the desired corner frequency of the high pass filter. Thefiltered second tone signal 126 is shown to have a second magnitude, orsignal strength, that is less than that of the filtered first tonesignal 124. The actual attenuation 118 is determined based on thedifference signal strength of the first and second filtered tone signals124 and 126, which is subsequently compared to the desired attenuation.Based on this comparison, the components of the high pass filter areadjusted to obtain the desired corner frequency.

FIGS. 6A and 6B illustrate the calibration of a bandpass filter. FIG. 6Aillustrates the frequency response of a first order bandpass filter thatincludes two attenuation regions and a pass region. The desired cornerfrequencies delineate the pass region from the two attenuation regions.The calibration of the bandpass filter is shown in FIG. 6B. Thecalibration begins by providing a first tone signal that has a frequencywell within the pass region. The filtered first tone signal 124 is shownto have a first magnitude or signal strength. The calibration continuesby providing a second tone signal that has a frequency at one of thedesired corner frequencies of the bandpass filter. The filtered secondtone signal 126 is shown to have a second magnitude, or signal strength,that is less than that of the filtered first tone signal 124. The actualattenuation 118 for this corner frequency is determined based on thedifference signal strength of the first and second filtered tone signals124 and 126, which is subsequently compared to the desired attenuation.Based on this comparison, the components of the bandpass filter areadjusted to obtain the desired corner frequency for this cornerfrequency. The calibration further includes providing a third tonesignal, that has a frequency at the other desired corner frequency ofthe bandpass filter. The filtered third tone signal 128 is shown to havea third magnitude, or signal strength that is less than that of thefiltered first tone signal 124. The actual attenuation 118 for thiscorner frequency is determined based on the difference signal strengthof the first and third filtered tone signals 124 and 128, which issubsequently compared to the desired attenuation. Based on thiscomparison, the components of the bandpass filter are adjusted to obtainthe desired corner frequency for this corner frequency.

FIGS. 7A and 7B illustrate the calibration of a stop band filter. FIG.7A illustrates the frequency response of a first order stop band filterthat includes two pass regions and an attenuation region. The desiredcorner frequencies delineate the attenuation region from the two passregions. The calibration of the stop band filter is shown in FIG. 7B.The calibration begins by providing a first tone signal that has afrequency well within the first pass region or the second pass region.The filtered first tone signal 124 is shown to have a first magnitude,or signal strength. The calibration continues by providing a second tonesignal that has a frequency at one of the desired corner frequencies ofthe stop band filter. The filtered second tone signal 126 is shown tohave a second magnitude, or signal strength, that is less than that ofthe filtered first tone signal 124. The actual attenuation 118 for thiscorner frequency is determined based on the difference signal strengthof the first and second filtered tone signals 124 and 126, which issubsequently compared to the desired attenuation. Based on thiscomparison, the components of the stop band filter are adjusted toobtain the desired corner frequency for this corner frequency. Thecalibration further includes providing a third tone signal that has afrequency at the other desired corner frequency of the stop band filter.The filtered third tone signal 128 is shown to have a third magnitude,or signal strength that is less than that of the filtered first tonesignal 124. The actual attenuation 118 for this corner frequency isdetermined based on the difference signal strength of the first andthird filtered tone signals 124 and 128, which is subsequently comparedto the desired attenuation. Based on this comparison, the components ofthe stop band filter are adjusted to obtain the desired corner frequencyfor this corner frequency.

FIG. 8 is a schematic block diagram of a calibration configuration forthe low pass filters (LPF) 86 of a radio receiver. In thisconfiguration, the output of a power amplifier 84 is coupled to theinput of the low noise amplifier 72. Thus, test signals (i.e., the tonesignals) may be inputted to the mixers of the up conversion module 82.The mixers mix the test signals with a local oscillation to produce RFsignals. The RF signals are received by the low noise amplifier 72 andprovided to the mixers of the down conversion module 70. The mixers ofthe down conversion module 70 mix the received RF signals with a localoscillation to produce base band, or low intermediate frequency, signalsthat include an in-phase component [I(t)] and a quadrature component[Q(t)]. The low pass filters 86-1 and 86-2 filter the in-phase componentand the quadrature component, respectively.

In this embodiment, the signal strength module 112 includes twointegrators 140 and 142, a summation module 145, two registers 146 and148, and a subtraction module 147. The integrators 140 and 142 integratethe absolute values of the filtered I and Q components to obtain acorresponding energy of the two components. The summation module 145adds the energy components together to obtain the measured signalstrength 144. If the signal being processed corresponds to the firsttone signal (i.e. the signal having a frequency well within the passregion of the filter), the measured signal strength 144 is stored in thefirst signal strength register 146. If, however, the signal correspondsto the second tone signal (i.e., the signal having a frequency at thedesired corner frequency), the measured signal strength is stored in thesecond signal strength register 148. Once the signal strengths of thefirst and second tone signals have been stored, the subtraction module147 subtracts the measured signal strength of the second tone signalfrom the measured signal strength of the first tone signal to producethe actual attenuation 118.

The comparator 114 compares the actual attenuation 118 with the desiredattenuation 120 to produce an indication of the filter response. Theresponse adjust module 116 interprets the output of, the comparator 114to generate the adjust filter response signal 122.

FIG. 9 is a logic diagram of a method for calibrating a filter thatbegins at step 150 where a filter filters a first signal having a firstfrequency to produce a first filtered signal, wherein the firstfrequency is in a known pass region of the filter. The filter malt be ofvarious embodiments including a low pass filter, a bandpass filter, ahigh pass filter, and/or stop band filter. The processing continues atstep 152 where the signal strength of the first filtered signal ismeasured to produce a first measured signal strength. The processingcontinues at step 154 where the filter filters a second signal having asecond frequency to produce a second filtered signal, wherein the secondfrequency is at a desired corner frequency of the filter. The processingcontinues at step 156 where the signal strength of the second filteredsignal is measured to produce a second measured signal strength.

The processing continues at step 158 where the first measured signalstrength is compared with the second measured signal strength todetermine whether the filter has attenuated the second signal by adesired attenuation value with respect to the first signal. If yes, theprocess proceeds to step 164 where the desired filter response isobtained. If not, the process proceeds to step 162 wherein the filterresponse of the filter is adjusted to produce an adjusted filterresponse. Once the filter response has been adjusted, the process mayrepeat at step 150 if the adjustment is based on an incrementaladjustment process.

FIG. 10 is a logic diagram of a method for calibrating a receiver lowpass filter that begins at step 170 where the filter response of thereceiver low pass filter is set to an initial state (e.g., to have thehighest corner frequency possible or the lowest corner frequencypossible based on adjustability of the low pass filter components). Theprocessing continues at step 172 where the receiver low pass filterfilters a first signal having a first frequency to produce a firstfiltered signal, wherein the first frequency is in a known pass regionof the filter. The process continues at step 174 where the signalstrength of the first filtered signal is measured to produce a firstmeasured signal strength. The processing then continues at step 174where the receiver low pass filter filters a second signal having asecond frequency to produce a second filtered signal, wherein the secondfrequency is at a desired corner frequency of the filter. The processingcontinues at step 178 where the signal strength of the second filteredsignal is measured to produce a second measured signal strength.

The process continues at step 180 where the first measured signalstrength is compared with the second measured signal strength todetermine whether the filter has attenuated the second signal by adesired attenuation value with respect to the first signal. If yes, theprocess proceeds to step 184 where the desired filter response isobtained. If not, the process proceeds to step 186 where the filterresponse of the receiver low pass filter is adjusted to produce anadjusted filter response. The process may then continue at step 172 withthe new settings for the low pass filter.

As one of average skill in the art will appreciate, the term“substantially” or “approximately”, as may be used herein, provides anindustry-accepted tolerance to its corresponding term. Such anindustry-accepted tolerance ranges from less than one percent to twentypercent and corresponds to, but is not limited to, component values,integrated circuit process variations, temperature variations, rise andfall times, and/or thermal noise. As one of average skill in the artwill further appreciate, the term “operably coupled”, as may be usedherein, includes direct coupling and indirect coupling via anothercomponent, element, circuit, or module where, for indirect coupling, theintervening component, element, circuit, or module does not modify theinformation of a signal but may adjust its current level, voltage level,and/or power level. As one of average skill in the art will alsoappreciate, inferred coupling (i.e., where one element is coupled toanother element by inference) includes direct and indirect couplingbetween two elements in the same manner as “operably coupled”. As one ofaverage skill in the art will further appreciate, the term “comparesfavorably”, as may be used herein, indicates that a comparison betweentwo or more elements, items, signals, etc., provides a desiredrelationship. For example, when the desired relationship is that signal1 has a greater magnitude than signal 2, a favorable comparison may beachieved when the magnitude of signal 1 is greater than that of signal 2or when the magnitude of signal 2 is less than that of signal 1.

The preceding discussion has presented a method and apparatus foraccurate calibration of on chip filters. As one of average skill in theart will appreciate, the concepts of the present invention work forhigher order filters than the ones presented in FIGS. 3-10. As one ofaverage skill in the art will further appreciate, other embodiments maybe derived from the teachings of the present invention without deviatingfrom the scope of the claims.

1. A method for calibrating a receiver low pass filter, the methodcomprises: setting filter response of the receiver low pass filter to aninitial state; filtering, by the receiver low pass filter, a firstsignal having a first frequency to produce a first filtered signal by:setting a transmit power level of a transmitter section to a nominalcalibration power level; enabling a receiver section, wherein thereceiver section includes the receiver low pass filter; enabling,subsequent to enabling the receiver section, the transmitter section;and transmitting, by the transmitter section at the nominal calibrationpower level, the first signal to the receiver section; wherein the firstfrequency is in a known pass region of the filter; measuring signalstrength of the first filtered signal to produce a first measured signalstrength, filtering, by the receiver low pass filter, a second signalhaving a second frequency to produce a second filtered signal, whereinthe second frequency is at a desired corner frequency of the filter;measuring signal strength of the second filtered signal to produce asecond measured signal strength; comparing the first measured signalstrength with the second measured signal strength to determine whetherthe filter has attenuated the second signal by a desired attenuationvalue with respect to the first signal; and when the filter has notattenuated the second signal by the desired attenuation value withrespect to the first signal, adjusting filter response of the receiverlow pass filter to produce an adjusted filter response.
 2. The method ofclaim 1, wherein the filtering the second signal further comprises:transmitting, by the transmitter section at the nominal calibrationpower level, the second signal to the receiver section.
 3. The method ofclaim 1, wherein the adjusting the receiver low pass filter responsefurther comprises: incrementally adjusting a time-constant of thereceiver low pass filter corresponding to the corner frequency toproduce the adjusted filter response; filtering, in accordance with theadjusted filter response, the second signal to produce a subsequentsecond filtered signal; measuring signal strength of the subsequentsecond filtered signal to produce a subsequent second signal strength;comparing the first measured signal strength with the subsequent secondmeasured signal strength to determine whether the receiver low passfilter has attenuated the second signal by the desired attenuation; andwhen the receiver low pass filter has not attenuated the second signalby a desired attenuation value with respect to the first signal,repeating the incrementally adjusting, the filtering, the measuring, andthe comparing until the receiver low pass filter has attenuated thesecond signal by the desired attenuation value.
 4. The method of claim1, wherein the measuring of the signal strength of the first and secondsignals further comprises at least one of: determining in-phasecomponent and quadrature component magnitudes of the first and secondsignals to produce the first and second signal strengths, respectively;determining a square of the magnitudes of the in-phase and quadraturecomponents of the first and second signals to produce the first andsecond signal strengths, respectively; determining a power level of thein-phase and quadrature components of the first and second signals toproduce the first and second signal strengths, respectively; determininga received signal strength indication of the in-phase and quadraturecomponents of the first and second signals to produce the first andsecond signal strengths, respectively.
 5. The method of claim 1, whereinthe adjusting the receiver low pass filter response further comprises:determining an actual attenuation value based on the first and secondsignal strengths; comparing the desired attenuation value to the actualattenuation value to determined an attenuation error; and adjusting thefilter response based on the attenuation error.
 6. A radio frequencyintegrated circuit comprises: a transmitter section operably coupled toconvert outbound baseband data into outbound radio frequency (RF)signals; and a receiver section operably coupled to convert inboundradio frequency (RF) signals into inbound baseband data, wherein thereceiver section includes a low pass filter that includes: low passfiltering circuit operable to substantially pass analog low intermediatefrequency (IF) signals having a frequency in a pass region and toattenuate analog low IF signals having a frequency outside the passregion; and calibration module operably coupled to the low passfiltering circuit, wherein the calibration module: measures signalstrength of a first filtered signal to produce a first measured signalstrength, wherein the low pass filtering circuit produces the firstfiltered signal by filtering a signal having a first frequency, whereinthe first frequency is within the pass region and wherein producing thefirst filtered signal includes setting a transmit power level of thetransmitter section to a nominal calibration power level, enabling thereceiver section, enabling, subsequent to enabling the receiver section,the transmitter section, and transmitting, by the transmitter section atthe nominal calibration power level, the first signal to the receiversection; measures signal strength of a second filtered signal to producea second measured signal strength, wherein the low pass filteringcircuit produces the second filtered signal by filtering a signal havinga second frequency, wherein the second frequency is at a desired cornerfrequency of the filter; compares the first measured signal strengthwith the second measured signal strength to determine whether the filterhas attenuated the second signal by a desired attenuation value withrespect to the first signal; and when the low pass filtering circuit hasnot attenuated the second signal by the desired attenuation value withrespect to the first signal, adjusting filter response of the low passfiltering circuit to produce an adjusted filter response.
 7. The radiofrequency integrated circuit of claim 6, wherein the filtering thesecond signal further comprises: transmitting, by the transmittersection at the nominal calibration power level, the second signal to thereceiver section.
 8. The radio frequency integrated circuit of claim 6,wherein the adjusting the low pass filter response further comprises:incrementally adjusting a time-constant of the low pass filtercorresponding to the corner frequency to produce the adjusted filterresponse; filtering, in accordance with the adjusted filter response,the second signal to produce a subsequent second filtered signal;measuring signal strength of the subsequent second filtered signal toproduce a subsequent second signal strength; comparing the firstmeasured signal strength with the subsequent second measured signalstrength to determined whether the filtered has attenuated the secondsignal by the desired attenuation; and when the low pass filter has notattenuated the second signal by a desired attenuation value with respectto the first signal, repeating the incrementally adjusting, thefiltering, the measuring, and the comparing until the low pass filterhas attenuated the second signal by the desired attenuation value. 9.The radio frequency integrated circuit of claim 6, wherein the measuringof the signal strength of the first and second signals further comprisesat least one of: determining in-phase component and quadrature componentmagnitudes of the first and second signals to produce the first andsecond signal strengths, respectively; determining a square of themagnitudes of the in-phase and quadrature components of the first andsecond signals to produce the first and second signal strengths,respectively; determining a power level of the in-phase and quadraturecomponents of the first and second signals to produce the first andsecond signal strengths, respectively; determining a received signalstrength indication of the in-phase and quadrature components of thefirst and second signals to produce the first and second signalstrengths, respectively.
 10. The radio frequency integrated circuit ofclaim 6, wherein the adjusting the receiver low pass filter responsefurther comprises: determining an actual attenuation value based on thefirst and second signal strengths; comparing the desired attenuationvalue to the actual attenuation value to determined an attenuationerror; and adjusting the filter response based on the attenuation error.